The project has examined a number of variables related to avoiding infectious disease in thousands of twins - both monozygotic (who are virtually genetically identical) and dizygotic (who share, on average, half of their genes - and their siblings. These data have allowed us to estimate the degree to which differences between people correspond with genetic differences between people versus environmental differences between people. Findings indicated that both tendencies to experience disgust and tendencies to be consciously concerned about germs have genetic bases, and that the genes underlying these traits partially overlap. However, we observed no evidence that being raised in the same household has any effect on either tendencies to experience disgust or tendencies to be concerned about germs. The above-mentioned work assessed the tendency to experience disgust, which is assessed via self-report instruments. Other work in the project examined how well these self-reports correspond with behaviors that are observable to others. Using self-other agreement methods used by personality psychology, our team recruited pairs of people who know each other (e.g. close friends, romantic partners) and had them complete self-report instruments of tendencies to experience disgust AND rate their partner on those exact same instruments. Results indicated that self-reports of tendencies to experience disgust correspond well with others' perceptions of how one experiences disgust. These results suggest that aspects of the behavioral immune system can influence how people are perceived. Existing work also suggests that the behavioral immune system can influence intergroup attitudes: specifically, openness to immigration. However, such work has not illuminated why disgust sensitivity might relate to anti-immigrant sentiments. We find that disgust sensitivity relates to negativity only toward immigrants who do not adopt local norms and customs. This result suggests that the behavioral immune system does not evaluate others based purely on group membership, but rather on similarity to cultural norms. Findings from these projects were published in international journals, including Clinical Psychological Science, Emotion, and Journal of Experimental Social Psychology, and they formed the basis of Annika Karinen's Ph.D. thesis.
A second threat of work from the project has assessed visual attention to and physiological responses to pathogen cues using methods often employed by cognitive psychologists. One project found that individuals allocate attention longer toward images portraying pathogen threats than toward images portraying physical violence threats. However, this allocation of attention is independent from tendencies to be disgusted by pathogen cues and by transient disgust (as elicited by an odor). Another project found that, while hungry, individuals are more willing to eat novel foods (which present unknown disease threats) than when sated, but their skin conductance and heart rate responses to images of pathogen threats do not change as a function of hunger. And another project found that tendencies to experience disgust toward pathogen cues also lead to greater visual attention toward technologies that neutralize pathogens (e.g. soap), but not toward images of pathogen threats. This line of research suggests that transient states and individual differences relate to downstream responses to pathogen cues, but they do not relate to early-level attention toward or sympathetic nervous responses to such cues. Hence, variation in responses to pathogen cues likely occurs later in cognitive processing. Findings from these projects were published in international journals, including Evolution and Human Behavior and Emotion, and other work is currently under peer review. This line of research formed the basis of Paola Perone's Ph.D. thesis.
A final line of work has examined how individuals learn and respond to foods, and how the behavioral immune system influences these responses. One series of studies tested whether foods are less appealing when paired with disgust-eliciting images relative to other negative images. Four studies did not reveal evidence for a specific link between disgust and food assessments, but they did reveal that foods are perceived as less appetizing when paired with generally negative stimuli. Another series of studies examined how people view meats from foreign cultures versus plants from foreign cultures. Findings indicated that people are much more negative toward foreign meats than foreign plants, and that this difference is strongest for individuals easily disgusted by pathogen cues. And another series of studies used data from twins to evaluate whether a background of consuming meats and plants as a child related to greater preferences toward meats versus plants in adulthood and greater openness to foreign meats and plants. Results indicated that childhood meat consumption indeed relates to adult meat preferences, but that these relations are almost entirely genetically rather than experientially mediated. This line of research formed the basis of Cagla Cinar's Ph.D. thesis, and work was published in Appetite and is currently under review at other journals.
